Many electronic enclosures provide adequate shielding characteristics over a limited range of frequencies, and even provide some degree of protection from corrosion in a limited, or controlled envirornnent. Wide range frequency protection can be provided by use of metal enclosures.
Many electronic enclosures are manufactured from sheet metals, such as aluminum or stainless steel. While these enclosures provide high shield attenuation over a wide range of frequencies, they are susceptible to corrosion in harsh environments, such as, high humidity and/or corrosive salt environments. Also, they are very heavy, due to the high density of the materials. Added corrosion resistance is provided by electro-chemical processing and/or corrosion resistant paints. These added processes are subject to cracking and peeling which will increase the possibility of corrosion, and high maintenance costs.
Other electronic enclosures are manufactured from molded plastics, such as, polyamides, polyester, nylon, and other copolymers. While these types of enclosures are lightweight and easily manufactured, polymers provide limited EMI shield attenuation. In order to provide adequate shield attenuation, these enclosures must be electro-chemically plated with a metallic substance, such as, copper, silver, nickel, or combinations of said materials. Said enclosure materials may be painted with a metallic filled paint, and in many cases a combination of metallic plating and paints. These enclosures provide limited, if any, corrosion resistance and are generally used in non-corrosive environments.
For many years, users of electronic enclosures have had to sacrifice some desired requirements in order to obtain more needed requirements. That is, if a user needs high shield attenuation over a wide range of frequencies, bat would also like to save space anti/or weight, they would sacrifice space/weight for the attenuation requirements. Likewise, other users may have sacrificed wide ranges of frequency for space and/or weight requirements.
In general, for installations in which there is great flexibility in space and weight considerations, or in a controlled environment where corrosion is not a consideration, effective EMI Shielded enclosures can be constructed from methods and materials well known in the art.
On the other hand, for installations of electronic enclosures, such as, mobile electronic systems, aircraft electronics, shipboard electronics, radio/telephone communications, missile guidance and control systems, space shuttle and space lab electronics, and the like, where wide ranges of frequency attenuation, space and weight, and harsh environments where corrosion is a major concern, there are few suitable materials from which to manufacture lightweight, corrosion resistant, high strength, high shield attenuation over a wide range of frequencies, electronic enclosures.
For many years, manufacturers and others have attempted to combine state of the art materials and technologies to produce a material that will provide lightweight, high attenuation, corrosion resistance, and high strengths for use as electronic enclosures. U.S. Pat. No. 4,916,016 describes a process for injection molding a polymerizing resin to the face of a metal foil or metal clad plastic foil. This process does not provide for corrosion resistance to the metal foil or film, and does not provide a solution to the problems of delamination or cracking trader stress. Others, such as, U.S. Pat. No. 4,474,685 and 4,566,990 describes processes for metal filling composite type molding compounds and conductive thermoplastic compounds. These processes genially sacrifice structural integrity and strength as the metal fiber composition increases to provide higher conductivities and shield attenuation.